1. Field of the Invention
The invention relates to footwear and, more particularly, to footwear constructed to dissipate electrostatic charges.
2. Description of the Invention Background
Static electricity is the accumulation of electric charge in an insulated body, most frequently caused by friction, but also by other means, such as induction etc. Electrostatic discharge (ESD) is the transfer of electric charge between two bodies, often accompanied by a visible spark, as in the familiar phenomenon of doorknob shock. While electrostatic discharge per se may not be immediately harmful to a human body, at least at level of voltage less than about 3000 volts, a discharge of much smaller voltage might be damaging to sensitive equipment, such as electronic components for computers and magnetic data carriers. A low volt electrostatic discharge may also ignite explosive gases. Accordingly, protection against ESD is required in the electronics and telecommunications industries and in other industries wherein sensitive electrical components or explosive materials are being handled.
ESD is of particular concern to the electronics industries. For example, if a quality control inspector carries a static charge during an inspection or testing operation, at a minimum, the accuracy of the test may be affected or, in worse cases, one or more sensitive components may be damaged. One method commonly employed to address this problem is the use of conductive footwear. By wearing a pair of conductive shoes, the person testing the electronic products is electrically grounded and the static charge is therefore eliminated. Various tests have shown that conductivity, more specifically, the impedance of a conductive shoe must be maintained within a certain range. One company in the computer and electronics industry recommends that the impedance of a conductive shoe be maintained within 106 ohms to 107 ohms. Other forms of grounding have been used to dissipate the electrostatic charge before it builds up to harmful levels. Such grounding measures include installing conductive or dissipative floors or stepping mats and/or wearing conductive wrist straps.
The efficacy of antistatic devices such as footwear, wrist and heel straps, etc. is typically determined by the electrical resistance of the conducting surface of the device in ohms. This electrical resistance may be affected by various environmental factors, such as humidity, dirt and other contamination, wear and other damage. A variable or unreliable electrical resistance does not provide continuous and reliable protection, as required in many environments with components sensitive to relatively small electrostatic discharges.
There remains, therefore, a need for footwear with improved electrostatic discharge properties that overcomes the limitations, shortcomings and disadvantages of the previous approaches.